This invention relates to a radio communication device for use with a mobile communication equipment for carrying out mobile communication such as a portable telephone and a transmission power control method in the radio communication device.
A mobile communication equipment such as a portable telephone generally used is equipped with a function of controlling its own transmission power in response to the distance between a base station and the mobile station when information is transmitted. In a communication system of multiple access type for multiplexing communication channels, transmission power control for fixing power of signals arriving at the base station is absolutely necessary to reduce interference between the communication channels and improve frequency use efficiency.
Particularly with mobile communication equipment adopting a CDMA (code division multiple access) system using spread spectrum modulation techniques, a number of users share a single frequency band, thus the possibility is high that a so-called far and near problem in which a signal having large power masks a signal having small power will occur, and a problem occurs in which a signal of any other station degrades the line quality of the home station as an interference wave. To solve this problem, hitherto, various transmission power control techniques have been examined; particularly, a transmission power control system with a closed loop is known as a transmission power control system for responding to an interference signal changing instantaneously. In the CDMA system, highly linear transmission power control in a wide range (for example, 70 to 80 dB) is required. Further, in a wide-band CDMA (W-CDMA) system being examined at present as a next-generation mobile communication system, accuracy requirement of transmission power at the large power time is high and transmission power control of higher accuracy is required.
FIG. 8 is a flowchart to show an example of a transmission power control method in a related art with a closed loop. For a base station and a mobile station to communicate with each other, the mobile station determines a transmission power control bit based on the reception power of a reception wave (desired wave) from the base station at step S101, inserts the transmission power control bit into a transmission signal, and transmits the resultant signal to the base station. The base station receives the signal transmitted from the mobile station, extracts the transmission power control bit from the reception signal at step S105, and controls a variable power amplifier in the base station as indicated in the transmission power control bit at step S106.
Likewise, the base station determines a transmission power control bit based on reception power of the reception wave from the mobile station at step S104, inserts the transmission power control bit into a transmission signal, and transmits the resultant signal to the mobile station. The mobile station receives the signal transmitted from the base station, extracts the transmission power control bit from the reception signal at step S102, and controls a variable power amplifier in the mobile station as indicated in the transmission power control bit at step S103.
Such transmission power control is performed, thereby making it possible to hold reception power almost constant at the base and mobile stations regardless of where the mobile station is located.
To perform transmission power control of high accuracy by the transmission power control method in the related art as described above, variable power amplifiers of high accuracy are required and need to be controlled with high accuracy. However, if an attempt is made to provide variable power amplifier control of high accuracy using variable power amplifiers of high accuracy, the circuit scale becomes large, the power consumption amount increases, and the system or the unit with the variable power amplifier becomes expensive. It may be difficult to cover a wide range of gain control while high accuracy is maintained with one variable power amplifier. Therefore, considering power consumption, portability, system (unit) costs, etc., various difficulties are involved in providing transmission power control of high accuracy by the transmission power control method in the related art.
It is therefore an object of the invention to provide a radio communication device that can provide transmission power control means for less consuming power in a simple configuration for improving accuracy of transmission power control and can be miniaturized with lower power consumption and a transmission power control method in the radio communication device.
To that end, according to the invention, there is provided a radio communication device having a transmission power control function of controlling power transmitted to a station to communicate with, the radio communication device comprising at least two variable power amplifiers, variable power amplification control means for controlling the variable power amplifiers, and switch control means for performing switch control for the operation of the variable power amplifiers in response to a target transmission power.
The radio communication device further includes transmission power detection means for detecting transmission power of the radio communication device output to the station to communicate with, and in that the switch control means compares the detected transmission power with a predetermined threshold value and switches the variable power amplifiers based on the comparison result.
Further, the switch control means finds the number of times the absolute value of the detected transmission power has changed successively in a positive or negative direction from a predetermined threshold value and switches the variable power amplifiers based on the number of times.
The radio communication device further includes transmission power control bit extraction means for extracting a transmission power control bit sent from the station to communicate with from a reception signal, and transmission power theoretical value update means for updating a theoretical value of transmission power of the radio communication device based on the transmission power control bit, in that the switch control means compares the theoretical value of the transmission power with a predetermined threshold value and switches the variable power amplifiers based on the comparison result.
Further, the switch control means finds the number of times the absolute value of the theoretical value of the transmission power has changed successively in a positive or negative direction from a predetermined threshold value and switches the variable power amplifiers based on the number of times.
The radio communication further includes transmission power detection means for detecting transmission power of the radio communication device output to the station to communicate with, in that the variable power amplification control means finds an increment or decrement for each control step of the detected transmission power and changes a controlled variable of the variable power amplifier in response to the magnitude of the increment or decrement.
The radio communication device further includes transmission power control bit extraction means for extracting a transmission power control bit sent from the station to communicate with from a reception signal, in that the variable power amplification control means determines a sign representing power increment or decrement set in the transmission power control bit and changes a controlled variable of the variable power amplifier in response to a sign change of the transmission power control bit.
According to the invention, there is provided a transmission power control method in a radio communication device for controlling power transmitted to a station to communicate with, the transmission power control method comprising a step of providing at least two variable power amplifiers, a variable power amplification control step of controlling the variable power amplifiers, and a switch control step of performing switch control for the operation of the variable power amplifiers in response to a target transmission power.
The transmission power control method further comprises the transmission power detection step of detecting transmission power of the radio communication device output to the station to communicate with, in that the switch control step compares the detected transmission power with a predetermined threshold value and switches the variable power amplifiers based on the comparison result.
Further, the switch control step finds the number of times the absolute value of the detected transmission power has changed successively in a positive or negative direction from a predetermined threshold value and switches the variable power amplifiers based on the number of times.
The transmission power control method further comprises the transmission power control bit extraction step of extracting a transmission power control bit sent from the station to communicate with from a reception signal, and the transmission power theoretical value update step of updating a theoretical value of transmission power of the radio communication device based on the transmission power control bit, in that the switch control step compares the theoretical value of the transmission power with a predetermined threshold value and switches the variable power amplifiers based on the comparison result.
The switch control step finds the number of times the absolute value of the theoretical value of the transmission power has changed successively in a positive or negative direction from a predetermined threshold value and switches the variable power amplifiers based on the number of times.
The transmission power control method further comprises the transmission power detection step of detecting transmission power of the radio communication device output to the station to communicate with, in that the variable power amplification control step finds an increment or decrement for each control step of the detected transmission power and changes a controlled variable of the variable power amplifier in response to the magnitude of the increment or decrement.
The transmission power control method further comprises the transmission power control bit extraction step of extracting a transmission power control bit sent from the station to communicate with from a reception signal, in that the variable power amplification control step determines a sign representing power increment or decrement set in the transmission power control bit and changes a controlled variable of the variable power amplifier in response to a sign change of the transmission power control bit.
In the radio communication device and the transmission power control method of the invention described above, switch control is performed for the operation of the variable power amplifiers in response to the target transmission power for controlling power transmitted to the station to communicate with. At this time, the variable power amplifiers are switched for operation in response to the transmission power, so that a wide accuracy in the simple configuration; the transmission power control accuracy can be improved, the operation of the variable power amplifier can be turned off for lower power consumption, and the unit can be miniaturized.
Further, in the radio communication device and the transmission power control method, the detected transmission power of the radio communication device or the theoretical value of the transmission power based on the transmission power control bit is compared with the predetermined threshold value and the variable power amplifiers are switched based on the comparison result. For example, switch control can be performed in response to the comparison result with one threshold value or more than one threshold value is provided and switch control can also be performed so as to prolong the time period over which the variable power amplifier operation is stopped, whereby power consumption can be reduced while the transmission power control is held accurate.
Furthermore, in the radio communication device and the transmission power control method, the number of times the absolute value of the detected transmission power of the radio communication device or the absolute value of the theoretical value of the transmission power based on the transmission power control bit has changed successively in the positive or negative direction from the predetermined threshold value is found and the variable power amplifiers are switched based on the number of times, whereby the time period over which the variable power amplifier operation is stopped can be prolonged, so that power consumption can be reduced while the transmission power control is held accurate.
Moreover, in the radio communication and the transmission power control method, the controlled variable of the variable power amplifier is changed in response to the magnitude of the increment or decrement for each control step of the detected transmission power or the sign change of the transmission power control bit representing power increment or decrement, whereby the error relative to the target transmission power can be reduced and the transmission power control accuracy can be improved for providing highly accurate transmission power.